Muffle furnace



June 7, 1927.

E. A. COLBY ET AL MUFFLB FURNACE Filed July 12, 1926 ATTORNEYS.

Patented June 7, 1927.

UNITED. STAT S 1,631,474 PATENT oF FicE.

EDWARD A. COLBY, 0E MAPL wooD; FREDERICK MAEULEN, OF EAST ORANGE; ANl) GEORGE L. VAN-ALLEN, 0F NEWa K, NEW JERSEY, ASSIGNORS T0 BAKER a com- IVANY, me, A CORPORATION or NEW JERSEY;

MUFFLE FURNACE.

Application filed July 12, 1926. Serial No. 121,792.

This invention relates particularly to i an electric mutlle furnace. for use in making artificial teeth. In the bakingoiartificial teeth certain basic. conditions: are, recognized as essential for the production ofj a-uniform roduct. ,1 First, relatively high temperature (13001400? C.) must .be maintained. over the whole mass of material "being-baked; second, a neutral or slightly oiridizinigatmosphere must exist within the chamber enclosing the teeth being, baked to ayoidvarx: ation in color shading, and:thir l; -the' 1naterial \vhile baking must-be. protected. from foreign material which. would at the baking temperature adhere to the surface of the teeth andxrnin the product, I

The maj orit-y'pf teetht day,.-are,.baked in oil-fired furnaces which are exceedingly in.- etiicient and objectionable on account ofthe hi h room temperature maintained. and; its efi ectupon operators and,the diflicult; of maintaining a id ing atmo p ere within the mufile andjtheprevalence of floating (lust which spoils the surfiacerof} the teeth. Attempts. have-been ,made also to; bake ,teeth with gas-fired ,furnaces butithese are op,en,to the same general objection. as oil-tired, furinaces, audit is also more difiicult to ,rnaintain a neutral or oxidizing .atmo sphere within the baking m l M y-J, ttemp s: haw-r een made ,to, substitute for furnaces electric furnaces of, theresistortype but to meet the ak pg o t ns t. is n s ssesx thatg the electric resistor first should have ;a melting temperature materially ,aboveithf to the teetliare tofbe subjeoted,,;aiidf.second, should be of a non-oxidizing, lcharla cter. This first requirement eliminates all' of the cheaper metals, of the..non-oxidiiiiig characteiu The other base metals'havingthe necessary high mel ting point-'nnfortunately oxidize. at a very low temperature .Wahave ou d th P a is h bei 'm e l u e as the ,electrical resistor for furnaces for. this particular work, andas thismetal is oflhigh intrinsic value. it;- is necessary. to so ,design a furnace that a ini ni num' amoirnt of this precious metal will be required.. -.Thisv means that the,,el ect ric resistor should be, placed as close as possible to the material. that is to be baked and so positioned with reference. to theexter nal walls of the furnac e ithat the loss oft n outwardly by radiation and conduction is reduced to a minimum." It is further necessary that the support for the electric resistor (in this case the muflle) should have a high electrical resistance at the working temperatures to avoid short circuiting of the resistor; it should not react chemically with the'resistor nor should it contain material which softens or flows at the maximum temperatureof baking. Very pure alundum. has been, found best to meet these several conditions, and inuffles made of this material, with as thin wall as possible and of an internal area as-small. as feasible to bring the source of the heat as close as possible to the product being baked, are wound with the electric resistor. through which the necessary current is passed. to attain the desired temperature.

. One object of the invention is to; provide a. muffle furnaceembodyingnovel. and improved features of constructionqwhereby the furnace can be easily and quickly assembled and, disassembled with aminimum possibilityof injury to the electric heating resisto when repairs are necessary. Another object is to providea muflie furnace which includes a -novel andimproved construction and combination of a ,rnullle-jand a casing orhousing therefor, the housing consisting of a. plurality of. easily; separable parts and enclosing the .mufile .without imposin its weight, thereon with an air. gap

heat insulation: between the housing. and the muflie-on all sides-except the bottom, isaid parts. being so related that the mufile can be uickly removed by disassembling. the hous- 1s v a Other objects-are to provide a mufile furnace of. the character described wherein the muflle is so shaped and-positioned as toinsure maximum concentration of developed heat .upon the material with minimumloss ofheat by radiation. and conduction to.the external walls of the furnace; to provide a simple, inexpensive, and durable muffle furnace, and to obtainother results and advantages as may be brought out by the following. description.

Referring to the accompanying drawings, inwhich corresponding and like parts are designated throughout the several views by the same reference characters,

' Figure 1 is a ical longitudinal sectional view through an electric inufile furnace embodying the invention, and' a Figure 2 is a front elevation partially in section with the closure plu, for the mufile removed. Specifically. describing the illustrated embodimcnt of the invention, the reference character A designates the base of the furnace which may consist of a pluralitry offire brick 1, said base being: substantially rectangular in plan and ha'ving-numnted thereon a vertical. metal casing.' 2 open at its top as at 3.

Arranged upon the base A- is a sub-base 4 which is preferably in the form of a flat tile having an upstanding:- flange'or rib 5 around three sides thereof. On the top of the sub-base 4 is a layer of powdered heat and electricity insulating'material 6 which maybe magnesia, and restingupon said layer of-"insulating materiahis a thin slab or plate 7 which maybe oft-he same'matcrial as the sub-base 4. This plate 7 forms a seat or support for a mufiie 8 which is substantially ellipticalrin 'croSs-sectionivith its bottom side slightly fiat to firmly rest upon the plate 7, said" r nuflle prefemblybeingi'of' the same material as thizsub-basie 4." ""Helically wrapped aroundthe mufile 'in the u's n'alfma'm ner is a ribbonfJfOfelectricityconducfing material; or ias'caaee platinum. whi'ch 's'erves as anQelectric-heating boil, the extremities of the ribbon being iietutned upon themselves as indicated at 10 and. having secured'tliereto by"s uita'ble;clamp s' 11 electric, wires or cords l2 .by"'whi'ch"the' coil is connected i-to the circuit. 3 f z i A chest 13 'whicliisprefe rabl'y of the same materialasth sub bas t'isinmznted pon saidsi1 b-%as withiifith'periineti'aI flange 5 on the sub-base a'iid in. spaflcednelatibiifto the mine; aiefs'h'ap of the eater substantially corresponding 'tb that tham'ame na sufficiently larger to alloiv'anx ti'r of'oh'e half inch? or mere between. the? top-iandisidje wans- 'ofit'he 'iii ufilef and" correspondingin terior walls. of the caves? It" will be ol'r served"'that-- this 'c'onstriictibh provides'the best heat insulationon the sides and top of the mufile, namely a 'sealed volumeo'f air, and alsdthat th'e roof or therhtifllehlielived the 'weightof th l ieavy 'heatinsulating 4 material above its cover and only bears the burdeiiojfits own roofaiid a m of .the e r'icircliiig resistor; This constrii'ct-ion materially'priilon g s the life of the' muffle.

I The cover c'oniprises'a top 130, sides 1 31= and a closed"endi132l""]:he hottom 'of the cover which rests upon thesub-bas'e isopen so that the. cover may be slipped over the mutile,

and the end' of t hecover corresponding to the open end ofthe muffle is also open. The top of the cover is provided with slots' l' l through whichthe extremities of the ribbon 9 may be passed outwardly from the mufile.

The side of the casing 2 correspondin to theopen endeofi the cove lviz andrniitil e 8 isprovided with-an opening 15-within' which is arranged a face block or tile 16 which has an opening 17- in substantial axial, ailincment with the opening in the muffle 8. A tilling tile oriblocktlfi is interposed between the face tile 16 and the end of the mullle and sub-base-4. the top and sides of the filling tile being spaced inwardly from the top and sides of the-face-tile a distance substantially equal to the thickness of the cover 13.1w indicated at '19: It will be notedthat the open endof the muttle- 8 and the correspond ingend' of the sub-base 4 are in juxtaposed relation.'aml the filling tile abuts said ends of'the mufile an'd'the sub-base to form an end wall for the casing. The filling tile alsohas an opening JO-in substantial alinement with the opening'li and the opening in the :nulile. A closure plug' 21 is provided for closing the opening- 17. and preferably the said opening and sa.id"plug are tapered toim'alte a wedge fit. Y'Vhen the furnace is'in op eration, the'joints' 22'. 23 between the cover 13 and the face block 16 and' filling' blo'cl: 18 are cemented; and the joint 24 between i the end of the muflle8'and the filling block is, also cemented. The filling block 18 is alsoj secured to the facebl'ofck' 16 as by ceifint: r

"Vent openings-28 are provided in the mufing '3tlin, the coverf.

In assembling the 'furna ceiif the mum; is

placed upon the plate"T t hroi gh the open top ofthe casing flfw hereupon thelj'oint 24 'is'jCIii elilt'e'd ,Tli c tivi" 13 is then laced upon thesiib ha's'e 4 and thejex tremities 10" of thl'aribbon outwardly througslr the l slats- 14; was aintsee and 2am ates res toitheextremities 10 of theribb on by; the

lit!

turned o'n'jairid ;the-"furuace beated to lilie de- My siredter nperature as indicated bythe thermocouple"proj ecting i'nt oi t he back. oliilthe niuffie; whereupon the plug: 21 is removed and thc tray carrying the teeth tobe baked 'isinserted into the muffie 2t replaced. In disa's'sernblin'gthe furnace for repairs.', the reverse operatiorr' of assembling takes place, the 'gr'anular ma'terial' being first permitted to new outwardlybyaction of gravity through discharge openings 26 m the casmg i These openings; are 'no'rmally closed by suitable gates s llcli' as Sliding plates 27 The clamps 11' arethen discon nected from the ends l0'o'f the ribbon and the joints 22 and 23 broken and the cover 13 removed, after which the joint 24 is broken and the muflle removed.

With this construction, it will be observed that the mufile can be easily and quickly placed in and removed from the furnace by simple disassembling of the housing or casing which consists of the base 4, cover 13, filling block 18 and face block 16. The joints between the cover 13 and the sub-base 4 filling block and face block are so arranged as to retard the escape of heat from the muffie and to prevent the sifting of the insulating material 25 into the mutlle; and furthermore, the particular construction of the casing is simple and inexpensive.

While we have shown and described the invention as embodied in certain details of construction, it will be understood that this is primarily for the purpose of illustrating the principles of the invention and that many modifications and changes may be made in said details by those skilled in the art without departing from the spirit or scope of the invention. Therefore. we do not desire to be understood as limiting ourselves exceptas required by the following claims when construed in the light of the prior art. A i

Having thus described the invention, what we claim 'is:

1. In a mufile furnace, the combination of a casing to receive a mufile and having an opening at its top to receive granular heat insulating material and an opening in one side, a muffle housing including a base having an end wall formed with a charging opening accessible through'said side opening of the casing,'a closure for said charging opening, and a muflle cover having an open bottom with its edges removably resting upon said base and one end open the edges of which separably abut said end wall of saidbase, a muffle removably mounted 1 upon saidbaseandahaving one open end the edges of which 'abut s aid end. wall of said base around said charging opening, the top, sides and other end of said muffle being in spaced relation to said cover to form a closed air heat insulating space between the mufile and said cover, an electric heating coil surrounding said mutlie, and granular heat insulating material in said casing surrounding said muffle housing, said muffle housing protecting said mutlle against the weight of said granular insulating material.

2. A mutile furnace comprising a base, a face block having an opening. a filling block secured to one side of said face block with its top and sides spaced inwardly of the top and sides of said face block, said filling block having an opening in alinement with said opening in the face block, a mufile removably mounted on said base with its open end abutting said filling block and in alinementwith said opening in the filling block, an electric heating coil surrounding said muflie. and a cover for the muifie having an open bottom with its edges removably resting upon said base and one open end the edges of which separably overliethe top and s des of said filling block and separably abut said face block, whereby said mufiie is wholly enclosed.

3. A mufile furnace comprising a base having an end wall formed with an opening and an upstanding flange extending around the other end and sides thereof, a closure for said opening, a muffle removably mounted on said base inwardly of said flange with its open end in abutting relation to said end wall and in substantial alinement with said opening in said end wall. a cover for said mufile having an open bottom with its edges removably resting upon said base and fitting in contacting relation within said upstanding flange, said cover having. one open end the edges of which are'adapted to separably abut said end wall of the base, the top, sides and other end of said cover being in spaced relation to said muffle whereby said mufile may be wholly enclosed within a closed air heat insulating space, and an electric heating coil. surrounding said muflle in contact therewith.

EDWARD A. COLBY.

FREDERICK MAEULEN.

GEORGE L. VAN ALLEN. 

